1. Field of the Invention
The present invention relates to quantization of the phase of a speech signal, and more particularly, to an apparatus for quantizing the phase of a speech signal using a perceptual weighting function and a method therefor.
2. Description of the Related Art
It is essential to refer to the perceptual characteristics of the human auditory to system with respect to the spectrum of a speech signal in speech encoding systems. However, little attention has been paid to the perceptual characteristics of phase information. Recently, some interesting research addressing the importance of the perceptual characteristics of phase information in a speech signal has been conducted. It has been shown that humans"" ability to distinguish different phase spectra is better than is often assumed.
In an apparatus for processing information on the phase of a speech signal disclosed in application Ser. No. 09/571,417 filed by the present applicant, a criterion was proposed to determine perceptually irrelevant phase information in a stationary section of a speech signal in the context of frequency domain representation of the speech signal. For harmonic signals, the criterion leads to the xe2x80x9ccritical phase frequencyxe2x80x9d, below which phase information is irrelevant to the perceived quality of the signal. As mentioned above, the speech signal phase information processing apparatus for distinguishing an important phase component was provided considering human auditory characteristics, so that the phase component of the speech signal is selectively coded or composed. However, there remain many problems to be solved in order to more effectively quantize the phase information.
One of them is how to effectively quantize the phase information above the critical phase frequency using the perceptual characteristics. In the present invention, use of the perceptual characteristics of the human auditory system for quantizing the phase of the speech signal will be provided.
To solve the above problems, it is an object of the present invention to provide an apparatus for quantizing the phase of a speech signal, which is capable of improving the quality of encoded speech by quantizing phase information using a perceptual weighting function, which makes phase quantization noise of a speech signal less than a predetermined just noticeable difference (JND) of phase, and a method therefor.
Accordingly, to achieve the above object, according to an aspect of the present invention, there is provided an apparatus for quantizing the phase of a speech signal using a perceptual weighting function, comprising a phase information extractor for obtaining the phase of each harmonic frequency in a speech signal represented by the discrete sum of periodic signals having different harmonic frequency components, a quantization noise shaping unit for controlling the amount of quantization noise of each phase using a perceptual weighting function, which makes quantization noise less than a predetermined just noticeable difference (JND) of the phase, a quantization bit assigner for assigning quantization bits to each phase according to the controlled amount of quantization noise, and a scalar quantizer for quantizing each phase by the assigned quantization bits.
According to another aspect of the present invention, there is provided another apparatus for quantizing the phase of a speech signal using a perceptual weighting function, comprising a phase information extractor for obtaining the phase of each harmonic frequency in a speech signal represented by the discrete sum of periodic signals having different harmonic frequency components, a perceptual weighting function calculator for calculating a perceptual weighting function using a result obtained by measuring the JND of the phase at each harmonic frequency for a harmonic tone having the fundamental frequency of the speech signal, a comparator for comparing a previously provided quantization estimation codebook with each phase by applying the perceptual weighting function, and a minimum value detector for detecting the minimum value among comparison values sequentially obtained from the comparator and outputting the index of the quantization estimation code book corresponding to the minimum value.
To achieve the above object, according to an aspect of the present invention, there is provided a method for quantizing the phase of a speech signal using a perceptual weighting function, comprising the steps of (a) obtaining the phase of each harmonic frequency in a speech signal represented by the discrete sum of periodic signals having different harmonic frequency components, (b) calculating a perceptual weighting function using a result obtained by the JND of the phase at each harmonic frequency for a harmonic tone having the fundamental frequency of the speech signal, (c) controlling the amount of quantization noise of each phase by calculating the amount of quantization noise from the perceptual weighting function of each phase, (d) assigning quantization bits to each phase according to the controlled amount of quantization noise, and (e) quantizing each phase by the assigned quantization bits.
According to another aspect of the present invention, there is provided a method for quantizing the phase of a speech signal using a perceptual weighting function, comprising the steps of (a) obtaining the phase of each harmonic frequency in a speech signal represented by the discrete sum of periodic signals having different harmonic frequency components, (b) calculating a perceptual weighting function using the result obtained by measuring the JND of a phase at each harmonic frequency for a harmonic tone having the fundamental frequency of the speech signal, (c) comparing a previously provided quantization estimation code book with each phase by applying the perceptual weighting function, and (d) detecting the minimum value among the comparison values sequentially obtained in the step (d) and outputting the index of the quantization estimation code book corresponding to the minimum value.